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<body>
<div class="document" id="c-bindings-for-xapian">
<h1 class="title">C# bindings for Xapian</h1>

<p>The C# bindings for Xapian are packaged in the <tt class="docutils literal">Xapian</tt> namespace
and largely follow the C++ API, with the following differences and
additions.  C# strings and other types are converted automatically
in the bindings, so generally it should just work as expected.</p>
<p>The <tt class="docutils literal">examples</tt> subdirectory contains examples showing how to use the
C# bindings based on the simple examples from <tt class="docutils literal"><span class="pre">xapian-examples</span></tt>:
<a class="reference external" href="examples/SimpleIndex.cs">SimpleIndex.cs</a>,
<a class="reference external" href="examples/SimpleSearch.cs">SimpleSearch.cs</a>,
<a class="reference external" href="examples/SimpleExpand.cs">SimpleExpand.cs</a>.</p>
<p>Note: the passing of strings from C# into Xapian and back isn't currently zero byte safe.  If you try to handle string containing zero bytes, you'll find they get truncated at the zero byte.</p>
<div class="section" id="unicode-support">
<h1>Unicode Support</h1>
<p>In Xapian 1.0.0 and later, the Xapian::Stem, Xapian::QueryParser, and
Xapian::TermGenerator classes all assume text is in UTF-8.  If you're
using Mono on UNIX with a UTF-8 locale (which is the default on most
modern Linux distributions), then Xapian appears to get passed Unicode
strings as UTF-8, so it should just work.  We tested with Mono 2.6.7
using the Mono C# 2.0 compiler (gmcs).</p>
<p>However, Microsoft and Mono's C# implementations apparently take
rather different approaches to Unicode, and we've not tested with
Microsoft's implementation.  If you try it, please report how well
it works (or how badly it fails...)</p>
</div>
<div class="section" id="method-naming-conventions">
<h1>Method Naming Conventions</h1>
<p>Methods are renamed to use the &quot;CamelCase&quot; capitalisation convention which C# normally uses.  So in C# you use <tt class="docutils literal">GetDescription</tt> instead of
<tt class="docutils literal">get_description</tt>.</p>
</div>
<div class="section" id="exceptions">
<h1>Exceptions</h1>
<p>Exceptions are thrown as SWIG exceptions instead of Xapian
exceptions. This isn't done well at the moment; in future we will
throw wrapped Xapian exceptions. For now, it's probably easier to
catch all exceptions and try to take appropriate action based on
their associated string.</p>
</div>
<div class="section" id="iterators">
<h1>Iterators</h1>
<p>The C#-wrapped iterators work much like their C++ counterparts, with
operators &quot;++&quot;, &quot;--&quot;, &quot;==&quot;, and &quot;!=&quot; overloaded.  E.g.:</p>
<pre class="literal-block">
Xapian.MSetIterator m = mset.begin();
while (m != mset.end()) {
  // do something
  ++m;
}
</pre>
</div>
<div class="section" id="iterator-dereferencing">
<h1>Iterator dereferencing</h1>
<p>C++ iterators are often dereferenced to get information, eg
<tt class="docutils literal">(*it)</tt>.  In C# these are all mapped to named methods, as
follows:</p>
<table border="1" class="docutils">
<colgroup>
<col width="45%" />
<col width="55%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Iterator</th>
<th class="head">Dereferencing method</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>PositionIterator</td>
<td><tt class="docutils literal">GetTermPos()</tt></td>
</tr>
<tr><td>PostingIterator</td>
<td><tt class="docutils literal">GetDocId()</tt></td>
</tr>
<tr><td>TermIterator</td>
<td><tt class="docutils literal">GetTerm()</tt></td>
</tr>
<tr><td>ValueIterator</td>
<td><tt class="docutils literal">GetValue()</tt></td>
</tr>
<tr><td>MSetIterator</td>
<td><tt class="docutils literal">GetDocId()</tt></td>
</tr>
<tr><td>ESetIterator</td>
<td><tt class="docutils literal">GetTerm()</tt></td>
</tr>
</tbody>
</table>
<p>Other methods, such as <tt class="docutils literal">MSetIterator.GetDocument()</tt>, are available unchanged.</p>
</div>
<div class="section" id="mset">
<h1>MSet</h1>
<p>MSet objects have some additional methods to simplify access (these
work using the C++ array dereferencing):</p>
<table border="1" class="docutils">
<colgroup>
<col width="47%" />
<col width="53%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Method name</th>
<th class="head">Explanation</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal">GetHit(index)</tt></td>
<td>returns MSetIterator at index</td>
</tr>
<tr><td><tt class="docutils literal">GetDocumentPercentage(index)</tt></td>
<td><tt class="docutils literal">ConvertToPercent(GetHit(index))</tt></td>
</tr>
<tr><td><tt class="docutils literal">GetDocument(index)</tt></td>
<td><tt class="docutils literal"><span class="pre">GetHit(index).GetDocument()</span></tt></td>
</tr>
<tr><td><tt class="docutils literal">GetDocumentId(index)</tt></td>
<td><tt class="docutils literal"><span class="pre">GetHit(index).GetDocId()</span></tt></td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="non-class-functions">
<h1>Non-Class Functions</h1>
<p>The C++ API contains a few non-class functions (the Database factory
functions, and some functions reporting version information), but C# doesn't
allow functions which aren't in a class so these are wrapped as static
member functions of abstract classes like so:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">Xapian::version_string()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Version.String()</tt></li>
<li><tt class="docutils literal"><span class="pre">Xapian::major_version()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Version.Major()</tt></li>
<li><tt class="docutils literal"><span class="pre">Xapian::minor_version()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Version.Minor()</tt></li>
<li><tt class="docutils literal"><span class="pre">Xapian::revision()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Version.Revision()</tt></li>
<li><tt class="docutils literal"><span class="pre">Xapian::Auto::open_stub()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Auto.OpenStub()</tt> (but is now deprecated)</li>
<li><tt class="docutils literal"><span class="pre">Xapian::Chert::open()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Chert.Open()</tt> (but is now deprecated)</li>
<li><tt class="docutils literal"><span class="pre">Xapian::InMemory::open()</span></tt> is wrapped as <tt class="docutils literal">Xapian.InMemory.Open()</tt> (but is now deprecated)</li>
<li><tt class="docutils literal"><span class="pre">Xapian::Remote::open()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Remote.Open()</tt> (both the TCP and &quot;program&quot; versions are wrapped - the SWIG wrapper checks the parameter list to decide which to call).</li>
<li><tt class="docutils literal"><span class="pre">Xapian::Remote::open_writable()</span></tt> is wrapped as <tt class="docutils literal">Xapian.Remote.OpenWritable()</tt> (both the TCP and &quot;program&quot; versions are wrapped - the SWIG wrapper checks the parameter list to decide which to call).</li>
</ul>
</div>
<div class="section" id="constants">
<h1>Constants</h1>
<p>The <tt class="docutils literal"><span class="pre">Xapian::DB_*</span></tt> constants are currently wrapped in a Xapian
class within the Xapian namespace, so have a double Xapian prefix!
So <tt class="docutils literal"><span class="pre">Xapian::DB_CREATE_OR_OPEN</span></tt> is available as
<tt class="docutils literal">Xapian.Xapian.DB_CREATE_OR_OPEN</tt>.
The <tt class="docutils literal"><span class="pre">Query::OP_*</span></tt> constants are wrapped a little oddly too:
<tt class="docutils literal"><span class="pre">Query::OP_OR</span></tt> is wrapped as <tt class="docutils literal">Xapian.Query.op.OP_OR</tt>.
Similarly, <tt class="docutils literal"><span class="pre">QueryParser::STEM_SOME</span></tt> as
<tt class="docutils literal">Xapian.QueryParser.stem_strategy.STEM_SOME</tt>.
The naming here needs sorting out...</p>
</div>
<div class="section" id="query">
<h1>Query</h1>
<p>In C++ there's a Xapian::Query constructor which takes a query operator and
start/end iterators specifying a number of terms or queries, plus an optional
parameter.
This isn't currently wrapped in C#.</p>
<!-- FIXME implement this wrapping! -->
<!-- In C#, this is wrapped to accept any C# sequence (for -->
<!-- example a list or tuple) to give the terms/queries, and you can specify -->
<!-- a mixture of terms and queries if you wish.  For example: -->
<!-- subq = xapian.Query(xapian.Query.OP_AND, "hello", "world") -->
<!-- q = xapian.Query(xapian.Query.OP_AND, [subq, "foo", xapian.Query("bar", 2)]) -->
<div class="section" id="matchall-and-matchnothing">
<h2>MatchAll and MatchNothing</h2>
<p>In Xapian 1.3.0 and later, these are wrapped as static constants
<tt class="docutils literal">xapian.Query.MatchAll</tt> and <tt class="docutils literal">xapian.Query.MatchNothing</tt>.</p>
<p>If you want to be compatible with earlier versions, you can continue to use
<tt class="docutils literal">new <span class="pre">xapian.Query(&quot;&quot;)</span></tt> instead of <tt class="docutils literal">xapian.Query.MatchAll</tt>
and <tt class="docutils literal">new xapian.Query()</tt> instead of
<tt class="docutils literal">xapian.Query.MatchNothing</tt>.</p>
<!-- FIXME: Need to define the custom output typemap to handle this if it -->
<!-- actually seems useful... -->
<!-- - - - - - - - -->
<!-- Enquire -->
<!-- - - - - - - - -->
<!-- There is an additional method `GetMatchingTerms()` which takes -->
<!-- an MSetIterator and returns a list of terms in the current query which -->
<!-- match the document given by that iterator.  You may find this -->
<!-- more convenient than using the TermIterator directly. -->
</div>
</div>
<div class="section" id="matchdecider">
<h1>MatchDecider</h1>
<p>Custom MatchDeciders can be created in C#; simply subclass
Xapian.MatchDecider, and define an
Apply method that will do the work. The simplest example (which does nothing
useful) would be as follows:</p>
<pre class="literal-block">
class MyMatchDecider : Xapian.MatchDecider {
    public override bool Apply(Xapian.Document doc) {
        return true;
    }
}
</pre>
</div>
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